Manufacture of particle board



July 2, 1968 B. POLOVTSEFF MANUFACTURE OF PARTICLE BOARD Filed Jan. 16,1967 5 Sheets-Sheet 1 llillllllllllllllllllllllllllllllllllllllll'lllllllllllll IIIHHIIIHIIIIIIIHHIIIIIIIIIHHII]HIIIIIIHIII July 2, 1968 B- POLOVTSEFF MANUFACTURE OFPARTICLE BOARD Filed Jan. 16, 1967 3 Sheets-Sheet 2 MOB/LE SPRAYERSYNCHRONlZED WITH CONVEYOR Q 0 i L .0 w mmwwwuv 5 July 2, 1968 B.POLOVTSEF'F MANUFACTURE OF PARTICLE BOARD 3 Sheets-Sheet 3 Filed Jan.16, 1967 J'HIHIHHHJH II I I III I HIHHIWIHWIIWH United States PatentOffice 3,3dLZ33 Patented July 2, lddfi 3,391,233 MANUFAETURE OF PARTICLEBOARD Boris Polovtseit, 165 Ahnners Road, Lyne, Chertsey, EnglandContinuation-impart of application Ser. No. 312,866,

Oct. 1, 1963. This application Jan. 16, 1967, fier. No. 699,366

13 Claims. (Cl. 264-113) ABSTRACT OF THE DHSCLOSURE A method ofmanufacturing boards from wood chips or from other particulatematerials, hereinafter referred to as particle board, which includesmixing the chips with a thermo-setting binder spreading the mix layerupon layer on a travelling conveyor surface to form a mattress, andconsolidating the mattress by compressing it in a press having heatedplatens..During the for ration of the mattress, liquid is sprayed ontothe chips forming the marginal portions or onto the chips forming one ormore layers with increased wetting towards the edges of the layers, sothat the rate of shrinkage is substantially constant throughout thecured board during and after the hot pressing.

CROSS-REFERENCES TO RELATED APPLICATIONS This application is acontinuation-inpart of my application Ser. No. 312,860, filed Oct. 1,1963, now abandoned, entitled Manufacture of Particle Board.

BACKGROUNI'J OF THE INVENTION This invention relates to the manufactureof particle board by consolidation under heat and pressure of a mattressof chips and thermo-setting binder.

Previously, particle board manufactured by compression of a mattress ofchips and binder in a press having heated platens was of uneventhickness, even though great care was taken to ensure that the mattresswas of even thickness throughout and the press platens exactly parallel.The centre portions of such boards were usually thinner than themarginals portions. If boards of even thickness were required, it wasnecessary to sand off the outer marginal areas. The variation inthickness is generally quite small, but in mass production the wastageof material in sanding off the marginal surfaces is substantial.Previous attempts to overcome this problem by inserting a concave fillerblock between the mattress and a platen of the press have not beencompletely successful.

SUMMARY OF THE INVENTION According to the present invention there isprovided a method of manufacturing particle board which includes mixingparticulate material with a thermo-setting binder, spreading the mixedparticles layer upon layer on a travelling conveyor surface that ismoving in a longitudinal direction to form a mattress, and consolidatingthe mattress under heat and pressure to form a board, wherein themarginal areas of the mattress are provided with a higher moisturecontent than the centre portion, so that the rate of consequentshrinkage is substantially constant throughout the cured board duringand after hot pressing.

The present invention arose from the belief by the Applicant that thevariation in thickness of particle boards obtained from mattresses ofconstant moisture content throughout, arose from shrinkage of the centreportion and swelling of the marginal portions after the board was curedin the press, the shrinkage commencing even betribution of moistureWithin the plane of the board, leaving the central area with a highermoisture content than the marginal areas. After the board is curedhowever, the Wet central portion shrinks due to drying while in the hotpress, immediately after the press has been opened, and after the boardhas left the press. The peripheral drier portions of the board swell dueto moisture absorption from the air and due to moisture migration fromthe central portion of the board.

The method of the invention compensates for the unequal loss of moistureof the cured board in the press and after leaving the press, byinitially wetting the marginal areas of the mattress prior toconsolidation of the mattress in the press so that the cured boardleaves the press with a substantially constant moisture contenthroughout. A board manufactured according to the invention will ofcourse, in common with all wooden articles, absorb moisture from andloose moisture to the surrounding atmosphere according to the relativehumidity of the surrounding air, but any shrinkage or swelling due tothis will occur equally throughout the board.

Ideally, the whole marginal area surrounding an approximately ellipticalcentral area of the mattress is moistened prior to the consolidation ofthe mattress by heat and pressure, with the moisture content graduallyincreasing from a minimum adjacent the central area to a maximum at theouter edges of the mattress. Satisfactory results can however beobtained by moistening marginal bands along the sides and ends of amattress, or even moistening only the marginal bands along the sides ina mattress in which the ratio of length to width is high.

In the method of the invention, liquid may be sprayed onto the chipswhich have just been deposited, or which are in course of being spreadonto the conveyor to form marginal areas of a mattress, while themattress is being formed.

One of the common practices in chip spreading is permitting the same tofall from hoppers onto spinning spiked horizontal rollers. The rollers,in spinning, fling the chips so that in falling they are depositedcontinuous- 1y layer upon layer to cover a predetermined area on aconveyor and build up the required mattress. It is as the chips arebeing thus deposited that water, a solution of binder or other liquid issprayed over them for the purpose of carrying out the present invention.

By introduction of a binder solution into the sprays, an additionaleitect of extra strong bond is achieved in the marginal areas which isbeneficial in preventing the crumblin of the mattress edges during itshandling by the conveyor and by the loader and during the pressingoperation prior to contact with the top platen of the press, and whichresults in a stronger board edge after pressing.

In addition to moistening the marginal areas of the mattress, one ormore layers of the mattress may be provided with a higher moisturecontent than adjacent layers in order to obtain different physicalproperties in the finished board. Conveniently, one or more selectedlayers may be provided with a higher moisture content than an adjacentlayer, with the marginal areas of the selected layer having a highermoisture content than the centre thereof and thereby ensuring asubstantially uniform rate of shrinkage of the board during and afterhot pressing.

Increasing the moisture content of different layers pro vides differentphysical properties for the boards due to the fact that, afterconsolidation of the mattress by heat and pressure, the layer or layershaving the increased moisture content are harder and denser than wouldbe the case if such layers were not intentionally moistened.

Water or other liquid may be sprayed onto the particles intended to formone or some of the middle layers of the board as such particles arefalling or have fallen BRIEF DESCRIPTION OF THE DRAWING FIGURE 1 is adiagram of the typical variation in thickness found in particle boardmanufactured according to previous known methods.

FIGURE 2 is a somewhat diagrammatic plan view of apparatus forlongitudinal and transverse Spraying of a mattress as it is beingformed, a portion of the apparatus and mattress thereon being brokenaway.

FIGURE 3 is a somewhat diagrammatic side elevational view of apparatusfor spraying selected layers of a mattress as it is being formed.

FIGURE 4 is a plan view of the structure shown in FIGURE 3, and

FIGURE 5 is a diagrammatic side elevational view of apparatus forspraying the middle layer of the mattress as the mattress is beingformed.

FIGURE 6 illustrates ditferent patterns of moisture in mattresses formedin the method according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The view in FIGURE 1 is a planof a particle board manufactured according to the previously practicedmethod in which the moisture in the mattress is distributed evenlythroughout prior to consolidation in the hot press. Marked on the planview are areas of different thickness, namely a central area A andconcentric bands B, C, D, which are approximately elliptical in shapeand surround the central area A. In a typical example of such a boardthe central area A may have an average thickness of 0.790 to 0.795 inchand bands B, C, D, may have average thicknesses of 0.800, 0.805, 0.810inch respectively, the thickness gradually changing from each area tothe adjacent areas.

The apparatus shown in FIGURE 2 enables mattresses to be formed with amoisture content which is greater in the marginal areas correspondingapproximately to bands B, C and D than in the central area A.

In FIGURE 2, there is illustrated a travelling conveyor 10 with a pairof spaced hoppers 11, 12 suspended thereabove for depositing on theconveyor separate layers of chips mixed with a thermo-setting binder,for example, a synthetic resin. The chips from hopper 11 are scatteredby spiked rollers in the direction of travel of the conveyor as shown at11a, and the chips from hopper 12 are scattered in the oppositedirection as shown at 12a. A stationary pipe 14 extending transverselyacross conveyor is provided with a jet overhanging each longitudinaledge portion of the conveyor to spray a liquid onto the chips depositedand being deposited from the hopper 11, the spray pattern for each jetbeing designated by 16a, 161) respectively. As a result, thelongitudinal edge portions 18 of the first layer 13 have a liquidsprayed thereon. A longitudinally reciprocating sprayer generallydesignated 21 is mounted for movement on means 22 in the direction ofdouble arrow 23, the movement of sprayer 21 in direction of arrow 27being in synchronism with the movement of the conveyor surface thatmoves in the direction of arrow 27. The sprayer 21 includes atransversely extending pipe 24 having a series of jets to spray theliquid onto the layer 13 in a sprayed pattern 25 that extendstransversely across the layer 13 and is flared outwards from the centreline of the layer towards the side edges thereof. The second hopper 12and its accompanying spiked roller deposit a second layer 13a of chipsover the aforementioned layer 13 to form the complete mattress.

In operation, the sprayer 21 travels forwards from left to right inFIGURE 2 at the same speed as the conveyor 1- with the pipe 24positioned directly over the transverse dotted line 26 along which thematerial on the conveyor is subsequently divided to form separatemattresses to be consolidated by heat and pressure in a press. Duringthis movement from left to right the sprayer 21 sprays liquid on to thelayer 13 in the spray pattern shown in FIG- URE 2. When the sprayer 21has reached its forward limit of travel, the sprayer is moved quicklyrearwards to the junction with the next succeeding mattress and againtravels forwards in synchronism with the conveyor to spray liquid in thepattern 25 along the dividing line 26. The means 22 for reciprocatingthe sprayer 21 is driven from the conveyor and can be of any suitableconstruction. Since the spray pattern 25 is flared outwards from thecenter line of the conveyor towards the side edges thereof, liquid issprayed across the transverse edges of the mattresses and also acrossthe corners of the mattresses. Through the use of sprayer 21 and sprayjets at pipe 14, the liquid is thus sprayed on to the longitudinal,transverse, and corner marginal areas of the mattress surrounding anapproximately elliptical center portio corresponding to the area A shownin FIGURE 1.

Although FIGURE 2 shows a mobile sprayer 21, it is to be understood thatif it is not desired to spray liquid on transverse edge portions, thesprayer 21 may be omitted, or with provision appropriate of a valve (notshown) in pipe 24 the spray from pipe 24 may be discontinued.

Referring to FIGURES 3 and 4, there is illustrated a continuoustravelling conveyor 30 wherein chips mixed with a thermo-setting binderare spread onto the conveyor by permitting the chips to fall from thehoppers 31, 32 and 33 respectively onto the spinning spiked horizontalrollers 34, 35 and 36 to respectively provide a face layer 37, a middlelayer 38, and a second face layer 39, of a mattress generally designated45. A transverse stationary pipe and a second stationary transverse pipe43, each having a plurality of jets, is extended across the conveyor tospray a liquid onto the layers 37 and 39 respectively and chips formingsaid layers as they are falling to increase the moisture content of saidlayers 37, 39 as the mattress is being built up on the conveyor. Thejets of pipes 40, 43 are positioned and adjusted so as to provide spraypatterns 40a, 43b, in which the intensity of spraying increases from thecentre area to the outer edges of the mattress being formed.

Referring to FIGURE 5 spaced hoppers 52, 52 permit chips mixed withbinder to fall therefrom onto the spinning spiked rollers 53, 53respectively which scatter the chips as shown at 54 and 55 to build up amattress 59 on the conveyor 58. A transversely extending stationary pipe56 (of a construction indicated for pipe 40) sprays a liquid onto thechips which have been deposited on the conveyor and also those which arein the course of being spread on the conveyor to form the mattress, theintensity of spraying increasing from the centre area of the mattress tothe outer edges thereof. As may be noted in FIG- URE 5 the spray patternof the liquid is such that it is sprayed on the particles forming themiddle layer or layers 62 of the mattress.

The liquid sprayed onto the mattress in accordance with any of theembodiments described above may be water, a solution of a binder, orother liquids. Water may be sprayed on to the central area of themattress and a binder solution sprayed on to the two longitudinalmarginal areas to provide an extra strong bond which prevents crumblingof the mattress edges during handling.

It is of course to be understood that the quantity of liquid added tothe marginal areas of the mattress is such that, after consolidation ofthe mattress and setting of the binder in a press having heated platens,the marginal areas of the board have substantially the same moisturecontent as the central portion of the board and consequently equal ratesof shrinkage when drying out during and aft-2r hot pressing. Thequantity of liquid to be added will depend on numerous factors such asthe moisture content of the chips, the quantity and moisture content ofthe binder, and on the design and operation of the press, and can bedetermined by one skilled in the art.

:FIGURE 6 shows cross sections of mattresses having different patternsof moisture content which result in particle boards of differentphysical characteristics, the parts of the mattress having increasedmoisture content being shown by shading lines. It will of course, beappreciated that the depth of the mattresses are shown enlarged relativeto their width in order to illustrate more clearly the moisturepatterns.

FIGURE 6(a) shows a cross section of a mattress in which the marginalareas through their entire depth are provided with a higher moisturecontent than the centre area of the mattress, the moisture contentincreasing from a minimum adjacent the centre area to a maximum at theouter edges. This mattress after consolidation by heat and pressure,provides a board of substantially even thickness and constant densitythroughout.

FIGURES 6(b) (c) (d) (e)(f) show mattresses in which one or more layersare provided with a higher moisture content than the remainder of themattress, the moisture content in each of such layers increasing fromthe centre towards the outer edges. After consolidation by heat andpressure, each board will have a substantially even thickness due to theexcess moisture in the marginal areas, and the moistened layers in theresulting boards will be harder and denser than would be the case ifsuch layers were not moistened.

FIGURE 6(1)) shows a mattress in which only the top layer of themattress is moistened. The resulting board has a top layer which isharder and denser than the remainder of the board and will thus bendalong this top layer when subjected to load.

FIGURE 6(0) shows a mattress in which the top and bottom layers aremoistened. This results in a board having maximum stiffness.

FIGURE 6 (d) shows a mattress in which the middle layer is moistened,resulting in a board having maximum symmetrical flexibility.

FIGURE 6=(e) shows a mattress in which the moistened layer is anintermediate layer between the middle layer and a surface layer,resulting in a board having asymmetrical stiffness and mediumflexibility.

FIGURE 60) shows a mattress in which the moistened layers areintermediate layers symmetrical about the middle layer of the mattress.This results in a board of medium flexibility of symmetrical stiffness.

Although I have shown and described specific constructions of apparatusfor carrying out the method of my invention, this has only been made byway of example. My invention, therefore, is not to be restricted exceptinsofar as is necessitated by the prior art and by the spirit of theappended claims.

I claim:

1. A method of manufacturing particle board which includes mixingparticulate material with a thermo-setting binder, spreading the mixedparticles layer upon layer on a traveling conveyor surface that ismoving in a longi tudinal direction to form a mattress, andconsolidating the mattress under heat and pressure to form a boardcharacterized in that liquid is sprayed on to the mixed particlesforming the marginal areas of at least one layer of the mattress, thespray pattern of the liquid being such that the moisture content of saidmarginal areas after spraying increases from a minimum near the innerzone to a maximum at the outer zone of said marginal areas, whereby therate of shrinkage is substantially constant throughout the board duringand after hot pressing.

2. The method of claim 1, characterized in that said liquid comprises asolution of an adhesive binder.

3. The method of claim 1 further characterized in that the liquid andparticles respectively comprise water and wood chips.

4. A method of manufacturing particle board which includes mixingparticulate material with a thermo-setting binder, spreading the mixedparticles layer upon layer on a traveling conveyor surface that ismoving in a longitudinal direction to form a mattress, and consolidatingthe mattress under heat and pressure to form a board, characterized inthat liquid is sprayed onto the longitudinal, transverse and cornermarginal areas of the mattress surrounding an approximately ellipticalcenter portion of the mattress so that said marginal areas of themattress have a higher moisture content than the center portion thereofand the rate of shrinkage is substantially constant throughout the boardduring and. after hot pressmg.

5. A method of manufacturing particle board which includes mixingparticulate materials with a thermo-setting binder, spreading the mixedparticles layer upon layer on a travelling conveyor surface to form amattress, and consolidating the mattress under heat and pressure to forma board, characterised in that at least one selected layer of themattress is provided with a higher moisture content than adjacentlayers, with the marginal areas of the selected layer having a highermoisture content than the centre thereof, so that the density of theselected layer is increased and the rate of shrinkage is substantiallyconstant throughout the board during and after hot pressing.

6. The method of claim 5, further characterised in that said selectedlayer is one of the face layers of the mattress, whereby the boardobtained by consolidation of the mattress under heat and pressure has asubstantially even thickness and a face layer which is appreciablyharder and denser than the remainder of the board.

7. The method of claim 5, further characterised in that the selectedlayers are the two face layers of the mattress, whereby the boardobtained by consolidation of the mattress under heat and pressure has asubstantially even thickness and two face layers which are appreciablyharder and denser than the remainder of the board.

8. The method of claim 5, further characterised in that said selectedlayer is the middle layer of the mattress.

9. The method of claim 5, further characterised in that said selectedlayer is an intermediate layer between the middle and a face layer ofthe mattress.

10. The method of claim 5, further characterised in that the saidselected layers are two intermediate layers symmetrical about the middlelayer.

lll. The method of claim 5, further characterised in that the selectedlayer is provided with the increased moisture content by spraying liquidonto the particles as they are being spread onto the conveyor to formthe selected layer.

12. The method of claim 11, characterised in that said liquid is sprayedin such a manner that the moisture content of the marginal areas of theselected layer of the mattress increases from a minimum at the innerzone to a maximum at the outer zone adjacent the edge of the mattress.

13. The method of claim 12, further characterised in that the moisturecontent in at least one area of the selected layer is increased byspraying a solution of an adhesive binder onto the particles beingsprayed onto the conveyor to form such an area, and furthercharacterised in that the moisture content in at least one other area ofthe selected layer is increased by spraying water onto the relatedparticles.

References Cited UNITED STATES PATENTS 2,453,679 I'll-1948 Stamm et al.161-262 2,583,618 1/1952 Weyerhaeuser 264-422 2,673,370 3/1954 Goss264-113 EARL M. BERGERT, Primary Examiner.

W. 'E. HOAG, Assistant Examiner.

